Recent discoveries have shown that the very largest Kuiper belt
objects - Eris, 2005 FY9 and Sedna - are coated in methane, and
may contain other volatile ices as well. New detailed observations
show that even within this class of volatile-rich bodies unexpected
differences exist in their surface compositions. 2005 FY9, a body
approximately 60% the size of Pluto, with a reflectance spectrum
similarly dominated by methane, has a surface depleted in molecular
nitrogen by at least an order in magnitude with respect to Pluto.
We find that the existence this new class of volatile-rich objects,
the lack of volatiles on most Kuiper belt objects, and even the
otherwise peculiar surface of 2005 FY9 can be explained as a
consequence of atmospheric escape of volatile compounds. While
previous studies of the surface compositions of objects in the
Kuiper belt have found no explainable patterns, atmospheric escape
appears to provide a first-order explanation of the range of surface
spectra seen on bodies in the outer solar system.

The possibility of interrelation between long-period comets and
2003 UB313, a recently discovered large Kuiper Belt body, is
investigated. For this purpose, 78 objects crossing the plane of
motion of this body at distances from 37.8 to 97.6 AU have been
selected from 860 long-period comets. The overpopulation of comets
with this characteristic is also considered. The plane of motion
of 2003 UB313 is compared with the orbital planes of other objects
in number of comet crossings in the specified distance interval or
in some parts of it. A statistically significant overpopulation of
elliptic and intermediate comets with the corresponding orbital
nodes has been established. Recently discovered and absolutely faint
comets show the best effect in this sense. The same is also true
for comets with osculating eccentricities e < 1. A similar result
is also obtained for comets with ``original''
a1 > 0.010000.
It is hypothesized that the 2003 UB313 family is present among the
78 comets. Four of them have aphelion distances from 37.8 to 97.6 AU.
An ellipticity is traceable in the distribution of some of the
78 distant nodes. This may be considered as a further argument for
the suggested hypothesis. Generally, the body 2003 UB313 may be
assumed to play a prominent role in injecting observable comets
from the transneptunian region.

Published in:
Solar System Research, 41, 46 (2007 February)

[Astronomicheskii Vestnik, 41, 51]

The Formation of Ice Giants in a Packed Oligarchy:
Instability and Aftermath

As many as 5 ice giants--Neptune-mass planets composed of 90%
ice and rock and 10% hydrogen--are thought to form at
heliocentric distances of 10-25 AU on closely packed orbits
spaced 5 Hill radii apart. Such oligarchies are ultimately
unstable. Once the parent disk of planetesimals is sufficiently
depleted, oligarchs perturb one another onto crossing orbits. We
explore both the onset and the outcome of the instability through
numerical integrations, including dynamical friction cooling of
planets by a planetesimal disk whose properties are held fixed. To
trigger instability and the ejection of the first ice giant in
systems having an original surface density in oligarchs of 1 gm/cm2, the disk surface density must fall
below 0.1 gm/cm2. Ejections are predominantly by
Jupiter and occur within yr. To eject more than
1 oligarch requires
gm/cm2. For certain
choices of and initial semi-major axes of planets, systems
starting with up to 4 oligarchs in addition to Jupiter and Saturn
can readily yield solar-system-like outcomes in which 2 surviving
ice giants lie inside 30 AU and have their orbits circularized by
dynamical friction. Our findings support the idea that planetary
systems begin in more crowded and compact configurations, like those
of shear-dominated oligarchies. In contrast to previous studies,
we identify
as the regime relevant for
understanding the evolution of the outer solar system, and we
encourage future studies to concentrate on this regime while relaxing
our assumption of a fixed planetesimal disk. Whether evidence of
the instability can be found in Kuiper belt objects (KBOs) is
unclear, since in none of our simulations do marauding oligarchs
excite as large a proportion of KBOs having inclinations
as is observed.

The physical surface properties of a trans-Neptunian Object is
believed to be mainly produced as a result of interplay between
irradiation from different kinds of cosmic rays and collisions.
Objects recently resurfaced by collisions are likely to have very
different physical properties from those of the bulk population.
In particular, pristine ices from the interior are expected to be
present on the surface. A possible way to identify a trans-Neptunian
object that has suffered a major collision is by investigating the
lifetime of the orbit near its present location. If the lifetime
is very short, a physical encounter is a possible way by which the
TNO has evolved into such a short lived orbit.

The goal of this investigation is to search for tracers of a young
surface on objects with very short orbital lifetimes in the
trans-Neptunian Belt. We are looking for any evidence that indicates
that they reached their current unstable orbits through collisions.
In particular, we have studied the case of (59358) 1999 CL158,
a trans-Neptunian object that currently has the most chaotic orbit
in the Classical Belt.

By numerically integration its orbit, we estimate that
(59358) 1999 CL158 has resided near its location for about
10 Myr. We have also obtained a near-infrared spectrum of
(59358) 1999 CL158 in the region between 1.43-1.96 microns
using the near infrared imager and spectrograph, NIRI, at Gemini
North 8-m telescope. These NIR observations are of the faintest and
smallest TNO so far observed.

We present the results of the search of ice-bands, such as CH4
and H2O, having found evidence of the presence of the first
mentioned molecule. The detection of methane implies that it must
be an abundant component of this object. Methane is also evidence
of a young surface, therefore we conclude that it is likely that
(59358) 1999 CL158 has experienced a recent collision or
collisions.

We have completed a low-inclination ecliptic survey for distant and
slow-moving bright objects in the outer solar system. This survey
used data taken over 34 months by the University of Arizona's
Spacewatch Project based at Steward Observatory, Kitt Peak. Spacewatch
revisits the same sky area every three to seven nights in order to
track cohorts of main-belt asteroids. This survey used a multiple-night
detection scheme to extend our rate sensitivity to as low as
0.012 arcsec hr-1. When combined with our plate scale and flux
sensitivity (), this survey was sensitive to Mars-sized
objects out to 300 AU and Jupiter-sized planets out to 1200 AU. The
survey covered approximately 8000 deg2 of raw sky, mostly within
10 of the ecliptic but away from the Galactic center. An
automated motion-detection program was modified for this multinight
search and processed approximately 2 terabytes of imagery into
motion candidates. This survey discovered 2003 MW12, currently
the tenth largest classical Kuiper Belt object. In addition, several
known large Kuiper Belt objects and Centaurs were detected, and the
detections were used with a model of our observational biases to
make population estimates as a check on our survey efficiency. We
found no large objects at low inclinations despite having sufficient
sensitivity in both flux and rate to see them out as far as 1200 AU.
For low inclinations, we can rule out more than one to two Pluto-sized
objects out to 100 AU and one to two Mars-sized objects to 200 AU.

Published in:
The Astronomical Journal, 133, 1247 (2007 April)

Irregular Satellites of the Planets: Capture Processes in the Early Solar System

All four giant planets in the Solar system possess irregular
satellites, characterized by large, highly eccentric and/or inclined
orbits that are distinct from the nearly circular, uninclined orbits of
the regular satellites. This difference can be traced directly to
different modes of formation. Whereas the regular satellites grew by
accretion within circumplanetary disks, the irregular satellites were
captured from initially heliocentric orbits at an early epoch.
Recently, powerful survey observations have greatly increased the
number of known irregular satellites, permitting a fresh look at the
group properties of these objects and motivating a re-examination of
the mechanisms of capture. None of the suggested mechanisms, including
gas-drag, pull-down, and three-body capture, convincingly fit the group
characteristics of the irregular satellites. The sources of the
satellites also remain unidentified.

Just to let you know that the 19 presentations at the TNO workshop
held in Nantes, France, on Jan 11-12 in connexion with the New
Horizons mission are now online. The aim of the workshop was taking
stock of the current astronomical, geophysical, and geological
activities related to the Pluto system and the TNOs in the French
research community, and also introducing the New Horizons instruments
and sequence of events to the participants.

Below are some chapters from the ``Kuiper Belt'' book (M.A. Barucci,
H. Boehnhardt,D. Cruikshank, and A. Morbidelli, eds.; University
of Arizona Press, Tucson, 2007). I will include other chapters in
later issues of the newsletter if they are submitted to me, as well
as an outline of the full book when it is published.

Detecting heat from minor planets in the outer solar system
is challenging, yet it is the most efficient means for constraining
the albedos and sizes of Kuiper Belt Objects (KBOs) and their progeny,
the Centaur objects. These physical parameters are critical, e.g., for
interpreting spectroscopic data, deriving densities from the masses of
binary systems, and predicting occultation tracks. Here we summarize
Spitzer Space Telescope observations of 47 KBOs and Centaurs at
wavelengths near 24 and 70m. We interpret the measurements using
a variation of the Standard Thermal Model (STM) to derive the physical
properties (albedo and diameter) of the targets. We also summarize
the results of other efforts to measure the albedos and sizes of KBOs
and Centaurs. The three or four largest KBOs appear to constitute a
distinct class in terms of their albedos. From our Spitzer results,
we find that the geometric albedo of KBOs and Centaurs is correlated
with perihelion distance (darker objects having smaller perihelia), and
that the albedos of KBOs (but not Centaurs) are correlated with size
(larger KBOs having higher albedos). We also find hints that albedo may be
correlated with with visible color (for Centaurs). Interestingly, if the
color correlation is real, redder Centaurs appear to have higher albedos.
Finally, we briefly discuss the prospects for future thermal observations
of these primitive outer solar system objects.

Binaries have played a crucial role many times in the history of
modern astronomy and are doing so again in the rapidly evolving
exploration of the Kuiper Belt. The large fraction of transneptunian
objects that are binary or multiple, 48 such systems are now known,
has been an unanticipated windfall. Separations and relative
magnitudes measured in discovery images give important information
on the statistical properties of the binary population that can be
related to competing models of binary formation. Orbits, derived
for 13 systems, provide a determination of the system mass. Masses
can be used to derive densities and albedos when an independent
size measurement is available. Angular momenta and relative sizes
of the majority of binaries are consistent with formation by dynamical
capture. The small satellites of the largest transneptunian objects,
in contrast, are more likely formed from collisions. Correlations
of the fraction of binaries with different dynamical populations
or with other physical variables have the potential to constrain
models of the origin and evolution of the transneptunian population
as a whole. Other means of studying binaries have only begun to
be exploited, including lightcurve, color, and spectral data.
Because of the several channels for obtaining unique physical
information, it is already clear that binaries will emerge as one
of the most useful tools for unraveling the many complexities of
transneptunian space.

The dust disks observed around mature stars are evidence that
plantesimals are present in these systems on spatial scales that
are similar to that of the asteroids and the KBOs in the Solar
System. These dust disks (a.k.a. ``debris disks'') present a wide
range of sizes, morphologies and properties. It is inferred that
their dust mass declines with time as the dust-producing planetesimals
get depleted, and that this decline can be punctuated by large
spikes that are produced as a result of individual collisional
events. The lack of solid state features indicate that, generally,
the dust in these disks have sizes greater than approximately
10 m, but exceptionally, strong silicate features in some disks
suggest the presence of large quantities of small grains, thought
to be the result of recent collisions.
Spatially resolved observations of debris disks show a diversity
of structural features, such as inner cavities, warps, offsets,
brightness asymmetries, spirals, rings and clumps. There is growing
evidence that, in some cases, these structures are the result of
the dynamical perturbations of a massive planet. Our Solar System
also harbors a debris disk and some of its properties resemble those
of extra-solar debris disks. From the cratering record, we can infer
that its dust mass has decayed with time, and that there was at
least one major ``spike'' in the past during the Late Heavy
Bombardment. This offers a unique opportunity to use extra-solar
debris disks to shed some light in how the Solar System might have
looked in the past. Similarly, our knowledge of the Solar System
is influencing our understanding of the types of processes which
might be at play in the extra-solar debris disks.

The Distant EKOs Newsletter is dedicated to provide researchers with
easy and rapid access to current work regarding the Kuiper belt (observational
and theoretical studies), directly related objects (e.g., Pluto, Centaurs), and
other areas of study when explicitly applied to the Kuiper belt.

Recent and back
issues of the Newsletter are archived there in various formats. The web
pages also contain other related information and links.

Distant EKOs is not a refereed publication, but is a tool for
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Publication or listing of an article in the Newsletter or the web page does
not constitute an endorsement of the article's results or imply validity of its
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Distant EKOs is not a substitute for peer-reviewed journals.

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